Читать книгу Sarcopenia - Группа авторов - Страница 47

The loss of MU largely correlates with the loss of muscle fibers in aging [22]. Autopsy work comparing the quadriceps muscle of younger and older men demonstrate a substantial reduction in the number of muscle fibers (~214 000) in the latter cohort [23]. A 12‐year longitudinal trial of older men also found a 14.7% decrease in the cross‐sectional area of the quadriceps muscle [24]. Regarding muscle fiber phenotypes, comparison of males and females between 15 and 83 years found a 25–35% loss in muscle mass with senescence [25]. Others have documented the same, by the sixth decade of life, the number of type II muscle fibers declined from ~60 to 30% in two separate studies [26, 27]. It should be noted that total muscle atrophy may not be specific to the loss of type II fibers alone; in the abovementioned longitudinal trial [24] there was a ~40–60% loss of type I fibers at age 75 compared with age 65. In saying this, the loss of type II fibers is suggested to occur at a more rapid rate, which is likely a direct consequence of the neuromuscular remodeling phenomenon.